The present invention relates to lasers and, more particularly, to lasers using a metal vapor or metal halide, including mercury halide, as the lasing medium in requiring short pulsed excitation.
When it was desired to apply short, high voltage pulses to an electroded, coaxial discharge laser to attempt to achieve high efficiency, certain problems were noted. A troublesome problem in the use of metal vapor in lasers lies in the high temperature required to develop sufficient metal vapor pressure, e.g. 1500.degree. C. for copper. It is known from an article by L. A. Weaver and E. W. Sucov in IEEE J. Quantum Electron, Volume QE-10 (1974), entitled "Superradiant Emission at 5106,5700, and 5782 .ANG. in Pulsed Copper Iodide Discharges", that sources of metallic vapor may also be derived from certain metal halides, such as copper iodide, where appropriate vapor pressure can be achieved at temperatures as low as 600.degree. C. That lasing occurs in such vapors is known, but, in practice, the laser vapor is chemically unstable. Pumping on the laser to remove gaseous impurities results in loss of halogen and, hence, in deposition of the metal component on cold walls. Other problems in such systems involve chemical reaction and subsequent erosion of electrode material and difficulty in providing seals between the envelope material (typically, fused silica or refractory envelope material) and the electrode connections.
In order to seal the tube and to maintain the required pressure of metal halides for laser pulse generation, it is necessary that the fill chemistry be such that metal halide is regenerated from the metal and halide atoms or molecules generated in the discharge. It is further necessary that a metal atom scavenging chemistry exist in the tube in order to prevent metal deposition on the cooler sections of the tube. The free energy of formation of copper iodide is negative at the temperatures of interest and, therefore, the kinetics of formation of CuI(s) from Cu(s)+I.sub.2 (g) should be favorable and copper metal should be unstable with respect to copper halide at the walls. If necessary, a slight excess of free halogen can be introduced into the laser tube prior to sealing to drive the reaction toward copper halide at the walls of the tube.
The above discussion applies to metal halide systems in which it is desired to achieve the free metal as the lasant. However, in certain situations, such as when using mercury halides, the mercury monohalide is the lasant in the molecular state.